U.S. Pat. No. 3,771,358 (Y. Yamano) discloses a testing apparatus for measuring the torque exerted by the take-up reel shaft of a tape recorder and also permits measurement of the torque applied in fast forward or rewind modes of operation. The embodiments of Yamano are all characterized by recording tape extending over the usual guide rollers at the forward corners of the cassette shell so that in use the tape will pass over the recording head and between a pich roller and drive capstan. The tape is driven as in a conventional cassette towards the take-up spool when the tape recorder is in a normal record/playback mode. The take-up spool comprises an outer ring around which the tape is wound and an inner ring linked to the outer ring through a helical torsion spring, the inner ring being adapted to be driven by the take-up spindle of the tape recorder. A pointer from the inner ring overlaps a portion of the outer ring on which a scale is inscribed so that in monitoring the applied torque, a reading is obtained depending on the displacement of the inner ring relative to the outer ring.
Thus in the normal record/playback mode, a measurement is made of the dynamic torque of the take-up spindle, the tape being advance over the capstan at a constanct rate and having a braking function on the outer ring which thereby lags the displacement of the inner ring which is driven by the take-up spindle.
For proper operation of a tape recorder it is essential that there is sufficient torque applied by the take-up spindle at normal operational speed for the tape between the capstan and the take-up spool to be alwyas under tension since otherwise the tape can jam. On the other hand the tension must not be so great as to risk tape breakage and by virtue of the calibration of the Yamano apparatus, a technician can set the torque within a desired range and a non-expert with the use of the device can determine whether, after a given period of service, the machine has retained a torque setting within an acceptable range. When the Yamano system is used to monitor applied torque for either rewind or fast forward, the tension or drag on the tape causes relative rotational movement between the outer ring and the inner ring, the extent of movement indicatiang the applicable torque and suitable calibration may be provided so this can be read.
Another proposal in the field of testing apparatus for cassette type tape recorders is that of German Patent Specification No. 1919371. For the purpose of monitoring the performance of the take-up spindle and the rewind spindle, respective spools are provided within the cassette case, the periphery of each spool being grooved so that a wire is wound around the spool with one end of the wire attached to a fixed mounting and the other end is attached to a helical extension spring. The machine is switched on and the test device merely indicates whether the applied torque exceeds a certain value by virtue of whether or not rotation of the spool occurs due to the applied torque overcoming the frictional forces imposed by the wire wrapped around the spool.
The test apparatus both of U.S. Pat. No. 3,771,358 and German No. 1919371 are both complex, involving many parts, and requiring considerable skill and labour for correct assembly. Furthermore German No. 1919371 necessitates careful adjustment of the fixed mounting of each of the wires so as to impose the correct frictional force on the spool but the device fails to indicate a measure of the torque but only indicates whether it exceeds a certain value; the device is also susceptible to change in characteristics with use and it is considered that the accuracy of this device cannot be high. Furthermore the function of the take-up spindle cannot be monitored to determine the torque applied respectively in take-up and fast forward modes.